Highly corrosion-resistant hot dip plated steel material excellent in surface smoothness

ABSTRACT

The present invention provides a plated steel material, said plated steel material having a plated layer which contains Al of 4% or more in mass, excellent in surface smoothness even when a cooling rate is low. In the present invention: a plated layer which contains Al of 4% or more in mass and has an Al-type intermetallic compound in an Al phase or abutting on an Al phase is formed on the surface of a steel material; in particular, high corrosion-resistance is secured in various environments by using a plated layer containing Al of 4 to 20% and Mg of 1 to 10% in mass with the balance consisting of Zn and unavoidable impurities or a plated layer containing Al of 4 to 20%, Mg of 1 to 10% and Si of 0.001 to 2% in mass with the balance consisting of Zn and unavoidable impurities; said plated layer contains an intermetallic compound having a melting point of 600° C. or higher by 0.001 to 0.5% in mass; and a plated steel material having an excellent surface smoothness is obtained by using an Al-type intermetallic compound wherein at least one of the lattice constants is in the range from 3 to 5 Å.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a national stage application of PCT Application No.PCT/JP03/00129 which was filed on Jan. 9, 2003 and published on Sep. 18,2003 as International Publication No. WO 03/076679 (the “InternationalApplication”). This application claims priority from the InternationalApplication pursuant to 35 U.S.C. § 365. The present application alsoclaims priority under 35 U.S.C. § 119 from Japanese Patent ApplicationNos. 2002-064303 and 2002-130792, filed Mar. 8, 2002 and May 2, 2002,respectively, the entire disclosures of which are incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a plated steel sheet and, inparticular, to a steel material having a particular surface smoothnessand being applicable to various applications such as steel sheets forhome electric appliances, automobiles and building materials.

BACKGROUND INFORMATION

Among plated steel materials most commonly used as having a goodcorrosion resistance, there are galvanized-type and aluminum-plated-typesteel sheets. Such plated steel sheets are used in various manufacturingindustries including the fields of automobiles, home electric appliancesand building materials. In addition to those, plated steel materials areused in various fields including plated steel wires and hot dip plating.In particular, steel materials to which Al-added plating is applied havea high corrosion resistance and, therefore, have been increasingly usedin recent years.

To improve the corrosion resistance of such galvanized-type steelsheets, the use of Zn—Al—Mg—Si hot dip plated steel sheets has beendescribed in Japanese Patent No. 3179446. Further, in Japanese PatentPublication No. 2000-064061, it was described that a painted steel sheetmore excellent in corrosion resistance can be obtained by adding one ormore elements of Ca, Be, Ti, Cu, Ni, Co, Cr and Mn to such a proposedZn—Al—Mg—Si hot dip plated steel sheet.

Further, Japanese Patent Publication No. H5-125515 describes that, whenTi is added to a Zn—Al hot dip plated steel sheet with the aim ofimproving the corrosion resistance of a galvanized-type steel sheet, thesteel sheet is excellent in resistance to black discoloration with age.Furthermore, Japanese Patent Publication No. 2001-295015 describes thata surface appearance is improved by adding Ti, B and Si to a Zn—Al—Mghot dip plated steel sheet.

However, with the aforementioned and with other disclosed plated steelsheets, surface smoothness is likely insufficiently secured.

In the case of a Zn—Al binary alloy, the eutectic point thereof is 6%Al-94% Zn in mass and, when an Al concentration is higher than that, anAl phase crystallizes as a primary crystal. Meanwhile, in the case of anAl—Si binary alloy, the eutectic point thereof is 87.4% Al-12.6% Si inmass and, when an Al concentration is higher than that, an Al phasecrystallizes as a primary crystal.

In the case of a Zn—Mg—Al ternary alloy, the ternary eutectic pointthereof is 3% Mg-4% Al-93% Zn in mass and when an Al concentration ishigher than this an Al phase crystallizes as a primary crystal. When asolidification speed of plating is sufficiently secured at the time ofhot dip plating, the plating solidifies before an Al phase grows largeand therefore surface smoothness does not deteriorate. In contrast, whena solidification speed of plating is low, the problem is that an Alphase grows large at first, causing ruggedness to form on a platedsurface and, as a result, the surface smoothness deteriorates.

Nevertheless, the technology described in the aforementioned JapanesePatent No. 3179446 generally does not take the problem of thedeterioration of surface smoothness into consideration. Further, thoughthe technology described in the aforementioned Japanese PatentPublication No. 2000-064061 may employ the addition of one or moreelements of Ca, Be, Ti, Cu, Ni, Co, Cr and Mn with the aim of improvingpost-painting corrosion resistance, the technology neither takes theproblem of the deterioration of surface smoothness into consideration,nor refers to an intermetallic compound. The technology described in theaforementioned Japanese Patent Publication No. H5-125515 does not takethe problem of the deterioration of surface smoothness intoconsideration. Furthermore, though the technology described in theaforementioned Japanese Patent Publication No. 2001-295015 employs theaddition of Ti and B with the aim of suppressing the formation andgrowth of a Zn₁₁Mg₂ phase that deteriorates surface appearance, thetechnology neither takes the problem of the deterioration of surfacesmoothness into consideration nor refers to an intermetallic compound.

SUMMARY OF THE INVENTION

The present invention has been addressed in the light of the aboveproblems and the object thereof is to provide a plated steel materialexcellent in surface smoothness even in the case of a high Alconcentration exceeding 4% in mass.

According to one exemplary embodiment of the present invention, a highlycorrosion-resistant hot dip plated steel material excellent in surfacesmoothness is provided. For example, on the surface of the steelmaterial, a plated layer is provided which contains Al of 4% or more inmass and has an Al-type intermetallic compound in an Al phase. Accordingto another exemplary embodiment of the present invention, the platedlayer may contains Al of 4% or more in mass and has an Al-typeintermetallic compound abutting on an Al phase.

The plated layer may contain Al of 4 to 20% and Mg of 1 to 10% in masswith the balance consisting of Zn and unavoidable impurities.Alternatively or in addition, the plated layer may contain Al of 4 to20%, Mg of 1 to 10% and Si of 0.001 to 2% in mass with the balanceconsisting of Zn and unavoidable impurities. On the surface of the steelmaterial, a plated layer containing an intermetallic compound may beprovided having a melting point of 600° C. or higher by 0.001 to 0.5% inmass.

According to still exemplary embodiment of the present invention, ahighly corrosion-resistant hot dip plated steel material excellent insurface smoothness may be provided. For example, at least one of thelattice constants of the intermetallic compound may be in the range from3 to 5 Å. The intermetallic compound can be one or more of an Ni—Al-typeintermetallic compound, a Ti—Al-type intermetallic compound, aZr—Al-type intermetallic compound and an Sr—Al-type intermetalliccompound. The intermetallic compound can also be one or more of TiAl₃,NiAl₃, Co₂Al₉, Co₄Al₁₃, CrAl₄, CrAl₇, Cr₂Al₁₁, Mn₄Al₁₁, MnAl₆, Al₁₁Ce₃,CeZn₂Al₂, Al₉Ir₂, Al₁₁La₃, Al₁₂Mo, NbAl₃, Al₂Se₃, TaAl₃, ZrAl₃,Zr₂ZnAl₃, Al₂Ca, Ti₇Al₆Si₁₂, FeNiAl₉, Fe₃NiAl₁₀, TiAl₂, TiAl, Ni₂Al₃,NiAl and SrAl₄. The Ti—Al-type intermetallic compound may beTi(Al_(1-X)Si_(X))₃.

All cited references are hereby incorporated herein by reference intheir entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a micrograph (magnification: 3,500) of a plated layer of aplated steel material which includes an intermetallic compound existingin an Al phase.

FIG. 1( b) is an illustration of an exemplary distribution state of eachstructure in the microphotograph of the plated layer of the plated steelmaterial of FIG. 1( a).

FIG. 2( a) is a microphotograph (magnification: 2,500) of the platedlayer of a plated steel material according to the present inventionwhich includes an example of the solidification structure of the platedlayer.

FIG. 2( b) is an illustration of the distribution state of eachstructure in the microphotograph of the plated layer of the plated steelmaterial according to the present invention.

DETAILED DESCRIPTION

The hot dip plated steel materials according to the present inventioncan include: a plated steel material characterized by having on thesurface thereof a plated layer which contains Al of 4% or more in massand has an Al-type intermetallic compound in an Al phase. A plated steelmaterial can also be includes which is characterized by having on thesurface thereof a plated layer which contains Al of 4% or more in massand has an Al-type intermetallic compound abutting on an Al phase.

According to one exemplary embodiment of the present invention, hot dipplating can mean a plating which uses metal prepared: by adding Al and,if necessary, further one or both of Si and Mg to a molten Zn bath; orby adding Si and, if necessary, additional one or both of Zn and Mg to amolten Al bath.

In a plating bath, besides the above components, Fe, Sb, Pb, Sn andunavoidable impurities may be contained individually or in combinationby 0.5% or less in mass. Further, even when Ca, Be, Cu, Co, Mn, P, B, Biand the third group elements are contained by 0.5% or less in mass intotal, the effect of the present invention is not hindered and rather,in some favorable cases, corrosion resistance is further improveddepending on the addition amount.

The reason why an Al content is limited to 4% or more in mass in thepresent invention is that, if an Al content is less than 4% in mass, theeffect of improving corrosion resistance is insufficient. Meanwhile,when an Al content is less than 4% in mass, an Al phase does notcrystallize as a primary crystal and therefore the problem of thedeterioration of smoothness does not arises. The upper limit of an Alcontent is not particularly regulated. However, it is desirable that anAl content is 95% or less in mass in order to avoid too high a platingbath temperature.

According to an exemplary embodiment of the present invention, an Alphase may be the phase that looks like an island or a dendrite having aclear boundary in a plated layer and the phase corresponds to, forexample, an “Al phase” (an Al solid solution that contains Zn in thestate of a solid solution) at a high temperature in an Al—Zn binaryphase equilibrium diagram. In such an Al phase at a high temperature,the amount of dissolved Zn varies in accordance with the concentrationof Al in a plating bath. An Al phase at a high temperature usuallyseparates into a fine Al phase and a fine Zn phase at an ordinarytemperature and it is reasonably estimated that the island shapeobserved at an ordinary temperature is the residue of the Al phase at ahigh temperature. The phase that derives from such an Al phase (calledan Al primary crystal) at a high temperature and retains the shape ofthe Al phase is called an Al phase in the present invention.

In the case of an Al phase of an Al—Si binary, Al—Zn—Si ternary,Al—Zn—Mg ternary, Al—Mg—Si ternary or Al—Zn—Mg—Si quaternary alloy, theamount of dissolved elements and also the shape of the phase at anordinary temperature vary in accordance with the variation of theconcentration in the alloy in a plating bath. However, in any of thecases, the Al phase retains the shape derived from an Al primarycrystal, is clearly identified under microscopic observation, and thusis called an Al phase in the present invention.

In this manner, plating of a poor surface smoothness represents a statewherein ruggedness is formed on the surface of a plated layer at theintervals of several tens micrometers to several millimeters and cansufficiently be observed visually. When the cross section of a platedlayer is observed with an optical microscope, the plated layer isclassified into the portions of thick plated layers and thin platedlayers and, in some extreme cases, the thickness of a thin portion isless than half that of a thick portion. The smoothness can be evaluatedby measuring the roughness in the wavelength range of 50 μm or more.

The reason why the position of an Al-type intermetallic compound in aplating layer may be limited to a position in an Al phase or a positionabutting on an Al phase in the present invention is that, with anintermetallic compound existing at a position other than the above,surface smoothness would not likely be improved.

The reason why an Al-type intermetallic compound existing in an Al phaseor abutting on an Al phase improves surface smoothness is presumablythat the inoculation effect, that an Al-type intermetallic compoundprovides, acts as the crystallization nucleus of an Al phase causes manyAl phases to crystallize even at a low cooling rate and thesolidification of a plated layer to become uniform.

Based on the investigation of Al phases in many plated layers,intermetallic compounds several micrometers in size were observed inmost of the Al phases or at portions abutting on the Al phases. Anexample of an intermetallic compound existing in an Al phase is shown inFIG. 1. FIG. 1( a) shows a microphotograph (magnification: 3,500) of theplated layer of a plated steel material according to an exemplaryembodiment of the present invention. FIG. 1( b) shows an illustration ofan exemplary distribution state of each structure in the microphotographof FIG. 1( a). As can be seen and understood from FIGS. 1( a) and 1(b),each structure can clearly be identified by a microphotograph of theplated layer of a plated steel material according to the presentinvention.

The size of an intermetallic compound is not particularly limited in theexemplary embodiment of the present invention. For example, the sizes ofthe intermetallic compounds may be 10 μm or smaller. The percentage ofAl phases in which intermetallic compounds exist is not particularlylimited either. It is desirable that the rate of Al phases whereinintermetallic compounds exist exceeds 10% of all Al phases.

Plated steel materials having a highly corrosion-resistant particularlyin various environments among those according to another exemplaryembodiment of the present invention include a plated steel materialcharacterized by having on the surface thereof a plated layer containingAl of 4 to 20% and Mg of 1 to 10% in mass with the balance consisting ofZn and unavoidable impurities or a plated layer containing Al of 4 to20%, Mg of 1 to 10% and Si of 0.001 to 2% in mass with the balanceconsisting of Zn and unavoidable impurities.

Some of the reasons why an Al content is limited to 4 to 20% in mass arethat, if it is less than 4% in mass, the effect of improving corrosionresistance is insufficient, that, within that range, the problem of thedeterioration of smoothness caused by the lack of the crystallization ofan Al phase as a primary crystal is avoided, and that, if it exceeds 20%in mass, the effect of improving corrosion resistance is saturated.

Some of the reasons why an Mg content is limited to 1 to 10% in mass isthat, if it is less than 1% in mass, the effect of improving corrosionresistance is insufficient and, if it exceeds 10% in mass, a platedlayer embrittles and thus adhesiveness deteriorates.

Si has the effect of suppressing the growth of an Fe—Al alloy layer andimproving plating adhesiveness. For that reason, it is effective to addSi when an Fe—Al alloy layer is likely to grow as in the case of a highplating bath temperature or a large Al content. Some of the reasons whyan Si content is limited to 0.001 to 2% in mass is that, if it is lessthan 0.001% in mass, the effect of suppressing the growth of an Fe—Alalloy layer in a plated layer is insufficient and, if it exceeds 2% inmass, the effect of improving adhesiveness is saturated.

According to an exemplary embodiment of the present invention, aZn—Mg—Al-type plated layer forms a metallographic structure containingone or more of a [Zn phase], an [Al phase] and a [Zn₂Mg phase] in thesubstrate of an [Al/Zn/Zn₂Mg ternary eutectic structure]. Then, aZn—Mg—Al—Si-type plated layer forms a metallographic structurecontaining one or more of a [Zn phase], an [Al phase], a [Zn₂Mg phase],an [Si phase] and an [Mg₂Si phase] in the substrate of an [Al/Zn/Zn₂Mgternary eutectic structure].

The [Al/Zn/Zn₂Mg ternary eutectic structure] can be the ternary eutecticstructure comprising an Al phase, a Zn phase and an intermetalliccompound Zn₂Mg phase. The Al phase which composes the ternary eutecticstructure corresponds to, for example, an [Al″ phase] (an Al solidsolution that contains Zn in the state of a solid solution and includesa small amount of Mg) at a high temperature in an Al—Zn—Mg ternary phaseequilibrium diagram. Such an Al″ phase at a high temperature usuallyappears in the state of separating into a fine Al phase and a fine Znphase at an ordinary temperature. Further, the Zn phase in the ternaryeutectic structure contains a small amount of Al in the state of a solidsolution and, in some cases, is a Zn solid solution wherein a smallamount of Mg is dissolved further. The Zn₂Mg phase in the ternaryeutectic structure is an intermetallic compound phase existing in thevicinity of the point indicated at about 84% in mass of Zn in the Zn—Mgbinary phase equilibrium diagram. As long as it is observed in the phasediagram, it is estimated that Si does not dissolve in each phase or,even if it dissolves, the dissolved amount is very small. However, sincethe very small dissolved amount cannot clearly be identified with anordinary analysis, the ternary eutectic structure composed of the threephases is expressed by the term [Al/Zn/Zn₂Mg ternary eutectic structure]according to the exemplary embodiment of the present invention.

Further, an [Al phase] can be the phase that looks like an island havinga clear boundary in the substrate of the aforementioned ternary eutecticstructure and the phase corresponds to, for example, an [Al″ phase] (anAl solid solution that contains Zn in the state of a solid solution andincludes a small amount of Mg) at a high temperature in an Al—Zn—Mgternary phase equilibrium diagram. In an Al″ phase at a hightemperature, the amounts of dissolved Zn and Mg vary in accordance withthe concentrations of Al and Mg in a plating bath. Such an Al″ phase ata high temperature usually separates into a fine Al phase and a fine Znphase at an ordinary temperature and it is reasonably estimated that theisland shape observed at an ordinary temperature is the residue of theAl″ phase at a high temperature. As long as it is observed in the phasediagram, it is estimated that Si does not dissolve in the phase or, evenif it dissolves, the dissolved amount is very small. However, as thevery small dissolved amount cannot clearly be identified with anordinary analysis, the phase that derives from the Al″ phase (called anAl primary crystal) at a high temperature and retains the shape of theAl″ phase is called an [Al phase] in the present invention. In thiscase, the [Al phase] can clearly be distinguished from the Al phasecomposing the aforementioned ternary eutectic structure undermicroscopic observation.

Furthermore, a [Zn phase] can be the phase that appears as an islandhaving a clear boundary in the substrate of the aforementioned ternaryeutectic structure and, in some actual cases, a small amount of Al andfurther a small amount of Mg may dissolve in the phase. As long as it isobserved in the phase diagram, it is estimated that Si does not dissolvein the phase or, even if it dissolves, the dissolved amount is verysmall. In this case, the [Zn phase] can clearly be distinguished fromthe Zn phase composing the aforementioned ternary eutectic structureunder microscopic observation.

Yet further, a [Zn₂Mg phase] can be the phase that looks like an islandhaving a clear boundary in the substrate of the aforementioned ternaryeutectic structure and, in some actual cases, a small amount of Al maydissolve in the phase. As long as it is observed in the phase diagram,it is estimated that Si does not dissolve in the phase or, even if itdissolves, the dissolved amount is very small. In this case, the [Zn₂Mgphase] can clearly be distinguished from the Zn₂Mg phase composing theaforementioned ternary eutectic structure under microscopic observation.

Still further, an [Si phase] may be the phase that looks like an islandhaving a clear boundary in the solidification structure of a platedlayer, for example, the phase that corresponds to primary crystal Si ina Zn—Si binary phase equilibrium diagram. In some actual cases, a smallamount of Al may dissolve in the phase and thus, as long as it isobserved in the phase diagram, it is estimated that Zn and Mg do notdissolve or, even if they dissolve, their dissolved amounts are verysmall. In this case, the [Si phase] can clearly be identified in theplated layer under microscopic observation.

In addition, an [Mg₂Si phase] can be the phase that looks like an islandhaving a clear boundary in the solidification structure of a platedlayer, for example, the phase that corresponds to primary crystal Mg₂Siin an Al—Mg—Si ternary phase equilibrium diagram. As long as it isobserved in the phase diagram, it is estimated that Zn and Al do notdissolve or, even if they dissolve, their dissolved amounts are verysmall. In this case, the [Mg₂Si phase] can clearly be identified in theplated layer under microscopic observation.

An example of the solidification structure of the aforementioned platedlayer is shown in FIGS. 2( a) and 2(b). FIG. 2( a) shows an exemplarymicrophotograph (magnification: 2,500) of the plated layer of a platedsteel material according to another exemplary embodiment of the presentinvention. FIG. 2( b) shows an illustration of the distribution state ofeach structure in the microphotograph of FIG. 2( a). As can beunderstood from FIGS. 1( a) and 1(b), each structure can clearly beidentified by a microphotograph of the plated layer of a plated steelmaterial according to the exemplary embodiment of the present invention.

According to the present invention, it may be desirable that the meltingpoint of an intermetallic compound contained in a plated layer is 600°C. or higher. One of the reasons why surface smoothness improves bycontaining an intermetallic compound having a melting point of 600° C.or higher is presumably that an intermetallic compound of a high meltingpoint acts as a nucleus of a crystal, [Al phase] crystals crystallize inquantity and, as a result the growth of [Al phase] crystals issuppressed.

One of the reasons why the content of an intermetallic compound having amelting point of 600° C. or higher is limited to 0.001 to 0.5% in massis that, if it is less than 0.001% in mass, the effect of improvingsurface smoothness is insufficient and, if it exceeds 0.5% in mass, anintermetallic compound concentrates on the surface of a plated layer andpoor appearance occurs.

A method of adding an intermetallic compound is not particularlyregulated and a method of mixing fine powder of an intermtallic compoundin a bath, a method of melting an intermetallic compound in a bath orthe like may be applied. In particular, a bath prepared by melting verysmall amounts of Ti, Ni, Co, Cr, Mn, Ce, Ir, La, Mo, Nb, Se, Ta, Zr, Ca,Sr, etc. in a Zn—Al alloy liquid at a temperature of 400° C. to 600° C.and adding the elements which crystallize as an intermetallic compoundduring solidification before an Al phase crystallizes is very effectivein improving surface smoothness.

In the case of a plated layer formed by hot dip plating in a bath towhich elements having aforementioned features are added, intermetalliccompounds composed one or more of TiAl₃, NiAl₃, Co₂Al₉, Co₄Al₁₃, CrAl₄,CrAl₇, Cr₂Al₁₁, Mn₄Al₁₁, MnAl₆, Al₁₁Ce₃, CeZn₂Al₂, Al₉Ir₂, Al₁₁La₃,Al₁₂Mo, NbAl₃, Al₂Se₃, TaAl₃, ZrAl₃, Zr₂ZnAl₃, Al₂Ca, Ti₇Al₅Si₁₂,FeNiAl₉, Fe₃NiAl₁₀, TiAl₂, TiAl, Ni₂Al₃, NiAl and SrAl₄ are contained inor beside an Al phase.

Such intermetallic compounds may also appear as islands having clearboundaries in the solidification structure of a plated layer. When anintermetallic compound is crystallized from an Si added bath, sometimesa small amount of Si may dissolve in the intermetallic compound or apart of Al contained in the intermetallic compound may be replaced withSi.

In the case of an intermetallic compound having a lattice constant closeto 4.05 Å, which is the lattice constant of Al in particular, aninoculation effect is likely to be obtained and, for that reason, it maybe desirable that at least one of the lattice constants of intermetalliccompounds is in the range from 3 to 5 Å.

As Al-type intermetallic compounds having the aforementioned features,an Ni—Al-type intermetallic compound, a Ti—Al-type intermetalliccompound, a Zr—Al-type intermetallic compound, an Sr—Al-typeintermetallic compound and the like, concretely NiAl₃, TiAl₃,Ti(Al_(1-X)Si_(X))₃, ZrAl₃, SrAl₄, etc., can be used.

As substrate steel materials in the present invention, not only steelsheets but also various steel materials including wire rods, shapes,sections, steel pipes, etc. can be used. As steel sheets, bothhot-rolled and cold-rolled steel sheets can be used and, with regard tosteel types too, various types of steels can be applied, such asAl-killed steels, ultra-low carbon steel sheets to which Ti, Nb, etc.are added, high-strength steels produced by adding strengtheningelements such as P, Si, Mn, etc. to the above steels, and stainlesssteels.

A method for producing a product according to an exemplary embodiment ofthe present invention is not particularly regulated and various methodssuch as continuous plating method for steel sheets, hot dip platingmethod for steel materials and wire rods can be applied. In the case ofapplying Ni pre-plating as the lower layer, a commonly adoptedpre-plating method may be applied. A product produced according to thepresent invention can secure a plating layer having a good surfacesmoothness even when a cooling rate is low, and therefore the effect ofthe exemplary embodiment of the present invention is conspicuous in hotdip plating and hot dip plating of a material having a large thicknesswherein a large cooling rate is hard to secure.

Though the deposition amount of plating is not particularly regulated, adesirable amount is 10 g/m² or more from the viewpoint of corrosionresistance and 350 g/m² or less from the viewpoint of workability.

Exemplary embodiments of the present invention are further explainedbelow on the basis of Examples.

EXAMPLE 1

Cold-rolled steel sheets 2.0 mm in thickness were prepared, subjected tohot dip plating for three seconds at 400° C. to 700° C. in a platingbath wherein the amounts of added elements were changed and to N₂ wipingfor adjusting the plated amount to 140 g/m², and then cooled at acooling rate of 10° C./sec. or lower. The compositions of the platedlayers of Zn-type plated steel sheets and Al-type plated steel sheetsthus produced are shown in Tables 1 and 2, respectively.

Smoothness was evaluated by measuring the roughness in the wavelengthrange of 50 μm or more and regarding the roughness of 2 μm or less asacceptable.

The plated steel sheets thus produced were polished at an inclination of10 degrees, an intermetallic compound was searched for by SEM, and theintermetallic compound was determined from the composition rate obtainedby EPMA. In the evaluation, when an Al-type intermetallic compound wasconfirmed in or beside an Al phase, it was judged to be acceptable.

The evaluation results are shown in Tables 1 and 2. In the cases of Nos.1, 6, 11, 16, 21, 26 and 31, an intermetallic compound was not containedin an Al phase and therefore smoothness was unacceptable. In all theother cases, good smoothness was obtained.

TABLE 1 Composition Inter- of hot dip metallic galvanized Latticeconstant of compound layer (wt %) Intermetallic compound (Å) in AlRoughness No. Al Mg Si compound a b c phase evaluation Remarks 1 5 —Unaccept. Unaccept. Comparable 2 5 TiAl₃ 3.8537 8.5839 Accept. Accept.Invented 3 5 NiAl₃ 6.598 7.352 4.802 Accept. Accept. Invented 4 5 ZrAl₃4.009 17.281 Accept. Accept. Invented 5 5 SrAl₄ 4.46 11.07 Accept.Accept. Invented 6 11 3 — Unaccept. Unaccept. Comparable 7 11 3 TiAl₃3.8537 8.5839 Accept. Accept. Invented 8 11 3 NiAl₃ 6.598 7.352 4.802Accept. Accept. Invented 9 11 3 ZrAl₃ 4.009 17.281 Accept. Accept.Invented 10 11 3 SrAl₄ 4.46 11.07 Accept. Accept. Invented 11 11 3 0.05— Unaccept. Unaccept. Comparable 12 11 3 0.05 Ti(Al0.85Si0.15)₃ 3.788.538 Accept. Accept. Invented 13 11 3 0.05 NiAl₃ 6.598 7.352 4.802Accept. Accept. Invented 14 11 3 0.05 ZrAl₃ 4.009 17.281 Accept. Accept.Invented 15 11 3 0.05 SrAl₄ 4.46 11.07 Accept. Accept. Invented 16 551.5 — Unaccept. Unaccept. Comparable 17 55 1.5 Ti(Al0.85Si0.15)₃ 3.788.538 Accept. Accept. Invented 18 55 1.5 NiAl₃ 6.598 7.352 4.802 Accept.Accept. Invented 19 55 1.5 ZrAl₃ 4.009 17.281 Accept. Accept. Invented20 55 1.5 SrAl₄ 4.46 11.07 Accept. Accept. Invented 21 55 3 1.5 —Unaccept. Unaccept. Comparable 22 55 3 1.5 Ti(Al0.85Si0.15)₃ 3.78 8.538Accept. Accept. Invented 23 55 3 1.5 NiAl₃ 6.598 7.352 4.802 Accept.Accept. Invented 24 55 3 1.5 ZrAl₃ 4.009 17.281 Accept. Accept. Invented25 55 3 1.5 SrAl₄ 4.46 11.07 Accept. Accept. Invented

TABLE 2 Composition Inter- of Al hot metallic dip plated Latticeconstant of compound layer (wt %) Intermetallic compound (Å) in AlRoughness No. Al Mg Si compound a b c phase evaluation Remarks 26 10 —Unaccept. Unaccept. Comparable 27 10 Ti(Al0.85Si0.15)₃ 3.78 8.538Accept. Accept. Invented 28 10 NiAl₃ 6.598 7.352 4.802 Accept. Accept.Invented 29 10 ZrAl₃ 4.009 17.281 Accept. Accept. Invented 30 10 SrAl₄4.46 11.07 Accept. Accept. Invented 31 6 10 — Unaccept. Unaccept.Comparable 32 6 10 Ti(Al0.85Si0.15)₃ 3.78 8.538 Accept. Accept. Invented33 6 10 NiAl₃ 6.598 7.352 4.802 Accept. Accept. Invented 34 6 10 ZrAl₃4.009 17.281 Accept. Accept. Invented 35 6 10 SrAl₄ 4.46 11.07 Accept.Accept. Invented

EXAMPLE 2

Cold-rolled steel sheets 2.0 mm in thickness were prepared, subjected tohot dip plating for three seconds at 400° C. to 600° C. in a Zn alloyplating bath wherein the amounts of added elements were changed and toN₂ wiping for adjusting the plated amount to 140 g/m², and then cooledat a cooling rate of 10° C./sec. or lower. The compositions of theplated layers of the plated steel sheets thus produced are shown inTable 3.

Smoothness was evaluated by measuring the roughness in the wavelengthrange of 50 μm or more and regarding the roughness of 2 μm or less asacceptable.

The evaluation results are shown in Table 3. In the cases of Nos. 1 and23, an intermetallic compound was not contained in the plated layersand, therefore, the smoothness was unacceptable. In all the other cases,good smoothness was obtained.

TABLE 3 Composition of hot dip galvanized layer (mass %) Inter- Inter-metallic metallic Roughness No. Mg Al Si compound compound evaluationRemarks 1 3 11 — Unaccept. Comparable 2 3 11 0.1 TiAl₃ Accept. Invented3 3 11 0.1 NiAl₃ Accept. Invented 4 3 11 0.1 Co₂Al₉ Accept. Invented 5 311 0.1 CrAl₇ Accept. Invented 6 3 11 0.1 MnAl₆ Accept. Invented 7 3 110.1 CeZn₂Al₂ Accept. Invented 8 3 11 0.1 Al₉Ir₂ Accept. Invented 9 3 110.1 Al₁₁La₃ Accept. Invented 10 3 11 0.1 Al₁₂Mo Accept. Invented 11 3 110.1 NbAl₃ Accept. Invented 12 3 11 0.1 Al₂Se₃ Accept. Invented 13 3 110.1 TaAl₃ Accept. Invented 14 3 11 0.1 Zr₂ZnAl₃ Accept. Invented 15 3 110.1 Al₂Ca Accept. Invented 16 3 11 0.1 Ti₇Al₅Si₁₂ Accept. Invented 17 311 0.1 FeNiAl₉ Accept. Invented 18 3 11 0.1 Fe₃NiAl₁₀ Accept. Invented19 3 11 0.1 TiAl₂ Accept. Invented 20 3 11 0.1 TiAl Accept. Invented 213 11 0.1 Ni₂Al₃ Accept. Invented 22 3 11 0.1 NiAl Accept. Invented 23 311 0.05 — Unaccept. Comparable 24 3 11 0.05 0.1 TiAl₃ Accept. Invented25 3 11 0.05 0.1 NiAl₃ Accept. Invented 26 3 11 0.05 0.1 Co₂Al₉ Accept.Invented 27 3 11 0.05 0.1 CrAl₇ Accept. Invented 28 3 11 0.05 0.1 MnAl₆Accept. Invented 29 3 11 0.05 0.1 CeZn₂Al₂ Accept. Invented 30 3 11 0.050.1 Al₉Ir₂ Accept. Invented 31 3 11 0.05 0.1 Al₁₁La₃ Accept. Invented 323 11 0.05 0.1 Al₁₂Mo Accept. Invented 33 3 11 0.05 0.1 NbAl₃ Accept.Invented 34 3 11 0.05 0.1 Al₂Se₃ Accept. Invented 35 3 11 0.05 0.1 TaAl₃Accept. Invented 36 3 11 0.05 0.1 Zr₂ZnAl₃ Accept. Invented 37 3 11 0.050.1 Al₂Ca Accept. Invented 38 3 11 0.05 0.1 Ti₇Al₅Si₁₂ Accept. Invented39 3 11 0.05 0.1 FeNiAl₉ Accept. Invented 40 3 11 0.05 0.1 Fe₃NiAl₁₀Accept. Invented 41 3 11 0.05 0.1 TiAl₂ Accept. Invented 42 3 11 0.050.1 TiAl Accept. Invented 43 3 11 0.05 0.1 Ni₂Al₃ Accept. Invented 44 311 0.05 0.1 NiAl Accept. Invented

INDUSTRIAL APPLICABILITY

The exemplary embodiments of the present invention makes it possible toproduce a plated steel sheet excellent in surface smoothness without theformation of ruggedness on the surface even when a solidification speedof plating is low and to provide a very excellent effect industrially.

1. A corrosion-resistant hot dip plated steel material having aparticular surface smoothness, comprising: at least one section having asurface; and a plated layer provided on the surface, the plated layercontaining Al of about 4% to 20% in mass and Mg of about 1% to 10% inmass, and comprising an Al phase and an Al-type intermetallic compound,with the balance of the plated layer in mass consisting of Zn andunavoidable impurities, wherein the intermetallic compound has a meltingpoint of at least 600° C. and lattice constants in the range of about 3Å to 5 Å, and wherein the intermetallic compound comprises about 0.001%to 0.5% by mass of the plated layer.
 2. The steel material according toclaim 1, wherein the plated layer contains Si of about 0.001% to 2% inmass.
 3. The steel material according to claim 1, wherein theintermetallic compound is at least one of an Ni—Al-type intermetalliccompound, a Ti—Al-type intermetallic compound, a Zr—Al-typeintermetallic compound, and an Sr—Al-type intermetallic compound.
 4. Thesteel material according to claim 1, wherein the intermetallic compoundis at least one of TiAl₃, NiAl₃, Co₂Al₉, Co₄Al₁₃, CrAl₄, CrAl₇, Cr₂Al₁₁,Mn₄ Al₁₁, MnAl₆, Al₁₁ Ce₃, CeZn₂Al₂, Al₉Ir₂, Al₁₁La₃, Al₁₂Mo, NbAl₃,Al₂Se₃, TaAl₃, ZrAl₃, Zr₂ZnAl₃, Al₂Ca, Ti₇Al₆Si₁₂, FeNiAl₉, Fe₃NiAl₁₀,TiAl₂, TiAl, Ni₂Al₃, NiAl, and SrAl₄.
 5. The steel material according toclaim 3, wherein the Ti—Al-type intermetallic compound isTi(Al_(1-x)Si_(x))₃.
 6. A corrosion-resistant hot dip plated steelmaterial having a particular surface smoothness, comprising: at leastone section including a surface; and a plated layer provided on thesurface, the plated layer including Al of about 4% to 20% in mass, Mg ofabout 1% to 10% in mass, with the balance of the plated layer in massconsisting of Zn and unavoidable impurities, and an Al-typeintermetallic compound abutting on an Al phase.
 7. The steel materialaccording to claim 6, wherein the plated layer contains and Si of about0.001% to 2% in mass.
 8. The steel material according to claim 6,wherein the intermetallic compound has a melting point of at least 600°C. and about 0.001% to 0.5% in mass.
 9. The steel material according toclaim 6, wherein at least one of lattice constants of the intermetalliccompound is in a range from about 3 Å to 5 Å.
 10. The steel materialaccording to claim 6, wherein the intermetallic compound is at least oneof an Ni—Al-type intermetallic compound, a Ti—Al-type intermetalliccompound, a Zr—Al-type intermetallic compound, and an Sr—Al-typeintermetallic compound.
 11. The steel material according to claim 6,wherein the intermetallic compound is at least one of TiAl₃, NiAl₃,Co₂Al₉ Co₄Al₁₃, CrAl₄, CrAl₇, Cr₂Al₁₁, MmAl₁₁, MnAl₆, Al₁₁Ce₃, CeZn₂Al₂,Al₉Ir₂, Al₁₁La₃, Al₁₂Mo, NbAl₃, Al₂Se₃, TaAl₃, ZrAl₃, Zr_(2 ZnAl) ₃,Al₂Ca, Ti₇Al₆Si12, FeNiAl₉, Fe₃NiAl₁₀, TiAl₂, TiAl, Ni₂Al₃, NiAl, andSrAl₄.
 12. The steel material according to claim 10, wherein theTi—Al-type intermetallic compound is Ti(Al_(1-x)Si_(x))₃.